I was working on my truck this weekend hoping to get the AC working again before it gets warm out. I thought that it would just need to be re-charged, O ya I bought this truck in December 2008, so I don't know much about it, just the issues I have taken care of and some troubleshooting.
As I was saying I originally thought it just needed some refrigerant added and it would work again. Well I was wrong and I even purged the R-12 to do the 134a retro kit, which makes me upset now. I have the factory service manual and electrical manual. I noticed the compressor would not kick on period when adding refrigerant. I know that there must be an electrical issue going on. I ran a jumper from the battery and bypassed the plug on the cycling switch, when I energized the dark green wire the clutch engaged and it sucked the coolant in the system. This to me means that the light green wire is not getting power to it and completing the circuit. Has anyone had any issues with their AC not working that wasn't the pump? It could be the cycling switch but I am inclined to think it may be some relay or some other electrical thing going on some where else? Any ideas? Thanks

 

well you went the hard way about things....the first thing I would have done would be to jump the cycling switch with a paper clip and add refigerant....adding power to the wiring loom could possibly have blown a fuse...........by jumping the cycling switch you can eliminate 2 problems at once....1 is the cycling switch bad.....2 am I getting power to the cycling switch....by bypassing the switch you eliminate the need for the proper amount of 134a thus telling you that the clutch works and the system is operating..............word of WARNING when you bypass the cycling switch you CAN overfill the system...when you get close to capacity unjump the cycling switch and plug it in and the system SHOULD work if not you may need a cycling switch

 

Hey chrisbmo2000, My first move after putting the volt meter on the cycling switch wires and clutch wires and see no voltage was to jump the switch. When I did that I still had nothing. The clutch never engaged on the compressor while trying to add the refrigerant. It was only after I added power from the battery did anything work. The only reason I added the power was because I was out of ideas and I know if I added power to the positive side it would tell me whether or not the thing worked. I am aware of basic operations of the hvac system, I have been building large industrial HVAC's for 5 yrs. I am not a technician for the hvac but I know what to avoid that will cause major problems. The Automotive set up has its differences but it is primarily on the electrical end.

I just realized you mentioned "by jumping the cycling switch you can eliminate 2 problems at once....1 is the cycling switch bad.....2 am I getting power to the cycling switch...." After jumping the switch with a clip I still had nothing, thus signaling to me I am not getting power to the cycling switch, when I added power from the battery it worked until I removed the power. Any take on this? What could be reasons I do not have power. Since I bought the truck in Dec. the A/C has been blinking on the temperature control display of the truck. I have just assumed up until now that it was low on coolant and I needed to add more.

 

now Im on the same page I have not had my hands on a 92 hvac in awhile but there should be a fuse or relay the schematic I have shows a fuse and relay....I would start at the HVAC control panel and check for power "in and out" the low pres switch gets its power from the A/c fuse......but you probably already know this from the manuels you have I would start at the control panel and go from there.

 

Yes, I figured there was a fuse or something going on. The problem I have is that I do not know where it would be and where to look. So that we are on the same page are you telling I should look at the control panel in the cab of the truck (the user interface) like an aftermarket stereo has a fuse in the back of it or something?

 

This may not be related at all, but I had a problem with the hvac head unit in my 89. It would blink, than go out. after a while it would come back on, but never actually control anything. what I found was the connector on the firewall, drivers side by inner fender well, was dry and corroded. my father-in-law, a retired master electrician for ford, ( I know, Ford, but he worked on everything) suggested that I clean it out with some electrical connection cleaner( about 5 bucks at the auto parts store) and add new dielectric grease. apparently, after 20 years, dielectric grease gets hard and turns brown/black. it took a whole can of cleaner, a pick, a gun cleaning "tooth brush" and alittle patience, but after I got it back together, everything started working. even if this has nothing to do with the proplem at hand, I'd recommend doing this to everyone.

 

the fuse should be in the fuse box and the user interface is where I would start checking for power in and out....I do belive it is a electrical/vacume cluster

 

Hey treadhead, thanks for the tip. Sometimes it truly IS a bad connection.

 

Ok today I disconnected the battery waited a few minutes and re-hooked it up. The AC blinking light went away and the compressor clutch kicked in and I was able to charge the system. Every thing works great. Thanks guys.